The kind folks at Graphic Simulations have put together a list of web sites hosting extra single-player and multiplayer content for Red Faction. Seven links to maps, mods, and more are currently posted.

The company's Red Faction FAQ describes how to use user-created maps:

To play a user map file, create a folder in your Red Faction folder called "user_maps". Then, inside the "user_maps" folder create three new folders. Label one folder "multi", label the second folder "single", and label the third folder "textures". Players will be able to play / join a game by placing a copy of the levels VPP file into the appropriate folder in the "user_maps" folder. Place SP (single player) maps in the "single" folder and DM (Death Match), Team DM, and CTF (Capture the Flag) maps in the "multi" folder.